The present invention relates to optical oscillators such as lasers, and more particularly to optical oscillators with compensation for undesirable effects.
One of the problems confronting designers of optical oscillators such as lasers has been birefringence, which is overcome by the present invention.
Pulse transmission mode (PTM) lasers have been employed to produce laser pulses having higher peak power and shorter duration than could be accomplished using conventional Q-switching techniques. Although such devices have served the purpose, they have not proven entirely satisfactory under all conditions of service because of loss of laser power due to birefringence effects. As the laser optical field increases, the laser rod is heated, resulting in thermally induced distortions in the rod which cause birefringence effects. The beam passing through such a distorted rod is converted from a single-polarization beam to a nonuniform, elliptically polarized beam incorporating two polarizations. As the beam passes repeatedly through the rod, the amplitudes of the two polarizations in the beam are increased differently and nonuniformly. The presence of two polarizations causes premature drainage and loss of the power of one polarization, reducing overall total laser output power. This problem is more pronounced with pulse transmission mode lasers than with other lasers because of the longer time allowed for oscillation, and the greater number of passes through the rod, involved with the former configuration.